In recent years, various techniques for watching a field around an automobile are disclosed. For example, an apparatus described in a republished patent document WO00/64175 (U.S. Pat. No. 7,161,616) has plural cameras on a subject vehicle that capture a field image around the subject vehicle in various angles, compose those images by shifting viewpoints for generating an overhead view of the subject vehicle, and displays the overhead view on the apparatus. Further, Japanese patent documents such as JP-A-2003-312415, JP-A-2005-5978, JP-A-2002-232948, JP-A-2006-107521, JP-A-2006-282111 disclose a field watch apparatus for monitoring surrounding vehicles condition around a traveling subject vehicle in the overhead view by applying a technique disclosed in the first patent document.
The field watch apparatuses disclosed in the second to fifth patent documents in the above description use only on-board image capture devices disposed on the subject vehicle for generating the overhead view, thereby making it difficult for a distant vehicle to be precisely displayed on a screen, due to smallness of a vehicle in the captured image. In particular, a vehicle approaching to the subject vehicle at a high speed may not be identified as a warning object until a remaining time to have a close contact is too small, due to difficulty of finding the approaching vehicle in the overhead view.